By Anne Verhallen, Soil Management Specialist (Horticulture)
Every time I see a bare field this time of year I just think – what a missed opportunity – an opportunity to get a cover crop in and build soil. Cover crops should be a key part of any soil maintenance package. Adding a cover crop into the rotation not only protects the soil over winter but also adds to the length of time that the soil has an active living root system.
Active and living are the key here. Roots take in water and nutrients from the soil but don’t forget plant roots continuously slough off and they also produce and secrete compounds back into the soil. These are called root exudates. These exudates can be waste materials from plant processes or they can be compounds with a known function like lubrication or defence. Research has shown that, in their own way plants continuously communicate with other plants and other organisms, often through these root exudates.
The exudates can be highly variable in quantity and composition, depending upon the age and health of the plant, soil type and nutrient availability. The greatest variety of compounds is in the lower molecular weight materials like amino acids, organic acids and simple sugars. Most of the exudates are larger molecules like proteins and complex sugars like polysaccharides. This helps to fuel the microbiology of the soil and in turn helps to create stable soil aggregates that are able to resist wind and water erosion while also adding carbon to the soil.
Research is starting to show that while the above ground plant growth helps prevent erosion it is the roots that build and maintain soil. Fall planted cover crops often don’t have a lot of top growth to see but root growth can be significant. Two week old radish and oat seedlings will have roots that are almost 30 cm in length.
In early to mid September, oats and barley can be planted with expectation of good growth. As September slides into October, switch to winter cereals like wheat, triticale or cereal rye to ensure continued growth as the soil cools.
The living roots of cover crops ensure that there is an active root zone outside of the main crop production times and add to the overall plant diversity in the field. Living roots help to build and maintain soil; supporting crop production while holding the soil in place through those fall and winter storms.